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Today we are answering an age-old very  scientific and important question:  

What if the moon crashes into earth? It’s more  interesting and weird than you probably think.  

Let’s start with the basics: Why isn’t the  Moon on its way to crash into us already?

We know that earth’s gravity pulls everything  towards it, including the Moon, but somehow,  

it stays up, as if suspended by some opposite  force. But there is no other force countering  

gravity - instead, the trick to staying up  is a ‘sideways’ motion that we call an orbit.

You see orbits every day: when you throw  a ball it makes a tiny little orbit.  

The only difference between that ball’s  orbit and the moon’s is that the ball  

eventually hits the ground.  Basically, the reason is speed.

If you could throw your ball fast enough, it  would bend around the world and come back to you.  

If there was no air slowing it down, it could  orbit forever. And this is what the moon does:

Falling sideways around earth, very fast, with no  air slowing it down. Orbiting earth every 27 days,  

at 3600 km/h. So for the moon to just stop  in its orbit and plummet to the earth would  

break more laws of physics than we have time  to explain. So how do we crash it into earth?

In a nutshell, to change an object’s  orbit, you need to change its speed,  

which changes where gravity takes it. But  even small changes require enormous forces,  

which is why all the large objects in  the solar system are so stable nowadays.

According to science, the moon is big and very  massive. Even igniting billions of rocket engines  

all over its surface would barely move the Moon. It looks like nothing short of magic will make  

the moon fall. So we’ll use a magic  spell that slows down the moon so much  

that it changes its orbit and spirals towards  earth. To get the most from the experience,  

the moon will take exactly one year before  it hits earth. Ready? 3. 2. 1. *Magic

Month 1

For the first few days, nothing really  changes. The moon gets a tiny bit brighter  

and scientists get confused, but the rest  of us don’t notice anything different.

The only noticeable real effect of  the moon on the earth are the tides.  

Tides exist because while earth pulls on the  moon, the moon’s gravity pulls back on the earth.  

Since the strength of gravity gets weaker  with distance, different parts of the earth  

feel a slightly different pull. Which  causes the earth, especially the oceans,  

to bulge when the moon is above them, and  contract a little on the sides when it’s  

not. As earth rotates every day underneath  the moon, the moon’s influence fluctuates,  

causing the water-level of the oceans to rise  and fall by about half a meter twice a day.

But with the moon drawing ever closer, high tide  gets higher every day. At first barely noticeable,  

within a month the moon has covered half the  distance to the earth and ocean tides have  

grown to 4 meters. Everyday high tide  comes and waves flood coastal cities.  

And there is no end in sight. With the moon  drawing ever closer, tides rise ever higher,  

inundating another city and more  inhabited land with salty water every day.

Month 2

By the end of month 2 the moon has covered  two-thirds of the distance to earth,  

and global infrastructure is crumbling as  tides rise above ten meters – displacing up  

to a billion people who happen  to live near the coastlines.

As ports become inoperable shipping grinds  to a halt. Not only will it slow down the  

delivery of Kurzgesagt products but  also less exciting things like food.  

Global communications fall into disarray – 95% of  the internet is carried by ocean-crossing cables,  

and while these largely don’t mind the water,  their terminals on land do. Living inland  

doesn’t guarantee safety either, tidal  bores cause rivers to flow backwards,  

carrying saltwater to contaminate  surface and groundwater supplies.

Gas shortages follow, as oil refineries near  the coast are abandoned. Countries are left  

with the supplies they had on their shelves  and strict rationing will begin. In the cities,  

chaos reigns during the  scavenging hours of low tide,  

while survivors take refuge in  highrises when the water returns.

Month 3

Three months in and the moon is  close enough to disrupt communication  

and navigation satellites. While it is normally  far too distant for its gravity to cause any  

major problems for our satellites, the closer  it gets the more warped their orbits become.  

As their fuel for orbital corrections runs  out, satellites careen out of control.

Month 4 - 5 On earth, the tides are  

rapidly growing to about 30 meters and will be  reaching 100 m in height in a few short weeks.  

At low tide, the ocean recedes hundreds of  kilometers, exposing the continental shelf  

like vast deserts, while at high tide walls of  water drown agriculture, houses and skyscrapers.

And now, almost five months in, the  apocalypse has finished its warm-up act.

Since the oceans are on average only 3 kilometers  deep, the tides have reached their maximum. Up  

until now, the water in the oceans could flow,  absorbing most of the moon’s gravitational  

squeezing, but now the earth itself is really  feeling the squeeze of the ever approaching moon.  

These aren’t so much tides of ‘water’, but  tides of ‘rock.’ The squeezing of the planet,  

combined with the weight of quintillions of tons  of water sloshing on and off the tectonic plates,  

creates enormous stresses below and begins to  cause earthquakes of increasing magnitude and  

intensity. It’s impossible to say how serious  these earthquakes might be or where they occur,  

but like a child jumping on their bed  until it breaks, no good can come of it.

Strong tidal forces lead to volcanism  on other planets and moons. On earth,  

squeezing the planet disrupts the  magma reservoirs inside the crust,  

triggering sizable, climate-altering eruptions in  Chile, New Zealand, Yellowstone, and elsewhere.

Meanwhile, watching patiently above is the moon.  Still no bigger in the sky than a small cloud.  

Within 75,000 km of earth, it is bright enough  to illuminate the night sky like twilight.

Month 6 - 7

After half a year, the moon is entering the space  once occupied by geosynchronous satellites where  

it orbits earth every 24 hours. It appears  to float at one spot in the sky, unmoving,  

cycling through a full set of phases every  day, but only visible to half the planet.  

With the moon ‘stationary’ above the  earth, the tides seem to freeze in  

place – half the world flooded, half with  its water seemingly returned to the sea,  

as if Earth is holding its  breath to prepare for the worst.

As the moon sinks further, you might wonder if  its gravity would overpower Earth’s, pulling you 

up and ending your misery? Fortunately not.  

The earth’s surface gravity is about  6 times stronger than the moon’s,  

so even if the moon were hovering right on top  of you, you would still stay on the ground.

On the moon things are different though: the near  side of the moon is more strongly affected by  

earth’s gravity, so during the next few months, it  starts to stretch forward towards the earth, into  

something of an egg, triggering deep moonquakes  as the lunar rock flexes and changes shape. Though  

barely noticeable now, this ‘squish’ will grow  to hundreds of kilometers in a matter of months.

Month 8 - 11

At this point the apocalypse has arrived and  we can summarize the months before the crash  

as “everybody left has a really bad time”.  The tides sweeping over the Earth slow down  

and then reverse their direction because the  moon now orbits earth faster than it rotates.

The planet will experience an abundance of  earthquakes and volcanism. Massive amounts of  

volcanic aerosols rise high into the stratosphere,  shiny enough to reflect sunlight back into space.  

What little light gets through is rust-red and  is periodically diminished by daily eclipses.  

The result is a rapid global cooling, with  acid rains and summer snows killing even  

the hardiest plants.The clock runs out  on civilization. Billions have perished  

while an egg-shaped moon is still drawing  closer. Let’s get ready for the grand finale.

Month 12

Finally, at the end of the year,, the moon  has reached the Roche limit. That’s the point  

where Earth’s gravitational pull on the Moon is  stronger than the Moon’s own gravity. Things on  

the lunar surface start falling towards Earth  and by the time it crosses 10,000 km the entire  

moon disintegrates into rubble, smearing itself  into a massive ring system around the earth.

Fortunately, the moon’s disintegration  means the misery on Earth has ended.  

No moon means the general apocalyptic nature  of things comes to a halt. The oceans recede,  

flowing off the land one last time.

Any survivors are treated to a view  of tremendous arches spanning the sky,  

glimmering in the sunlight, illuminating  the night sky more brilliantly than any  

full moon ever could, while meteor  showers of moondust fill the sky.

It’s hard to say what happens next,  but the tranquility may be short-lived.  

If too much moondust rains down, friction  heats the atmosphere – possibly boiling the  

oceans. If not, the enormous  shadows cast by the rings,  

combined with all the volcanic and meteoric  aerosols, block even more sunlight,  

and a period of runaway cooling could begin  that freezes much of earth’s surface solid.

In any case, at some point people will  emerge again – from submarines or bunkers  

or mountaintops. They will not have a great time  before rebuilding civilization and their success  

is not guaranteed – but at least they will  try to do so with beautiful rings in the sky.

So how do you calculate that sort of thing? Well,  

you just need a bit of insanity and some  maths. If you need to brush on the latter:  

Our friends from Brilliant are the perfect coaches  to turn your curiosity into practical skills.

Brilliant is a problem-solving website  and app that makes science accessible 

with a hands-on approach. More than 60 interactive  courses like „The joy of problem solving“ or  

„Scientific thinking“ give you the tools to crack  problems in math, science and computer science in  

a way that feels more like playing a game than  doing homework. Lessons will surprise you with  

storytelling, code-writing tasks and interactive  challenges – basically using whatever keeps you  

interested and entertained. All the content is  interactive: instead of just reading and listening  

to explanations, you drag and drop, manipulate  shapes and diagrams, make selections and answer  

questions. This way you learn something almost  without you noticing it. And tiny step by step  

you’ll build up your long-term understanding  of science and get closer to your STEM goals.

To start looking at the world of  science from a different perspective,  

go to Brilliant.org SlashNutshell and sign  up for free. And there’s an extra perk for  

kurzgesagt viewers: the first 200 people to use  the link get 20% off their annual membership,  

which unlocks all of Brilliant’s courses  in math, science, and computer science.

At kurzgesagt we love to create things that seem  

impossible at first – Brilliant can  help you acquire the skills to do that.

This year we will release 3 very special limited  edition pins. The first one is this very shiny  

Moon Crash Pin Set. Pre-order is available  for only 72h, so you can order it now and then  

never again. Be sure to watch out for pin number  2 and 3 to complete your 12,022 collection.